This is an alternative to D66980, which was reverted. Instead of
inserting a pseudo instruction that optionally expands to nothing, add a
pass that inserts int3 when appropriate after basic block layout.
Reviewers: hans
Differential Revision: https://reviews.llvm.org/D67201
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@371466 91177308-0d34-0410-b5e6-96231b3b80d8
